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1993 K75S Dead Electric System

I have purchased a new to me 93 k75s .When i purchased the bike it neede a few repairs but the bike ran and started . The only indication orf a problem was the ABS light and the hazard warning light was on.
I replaced both the leaking brake lines front and rear and found a bad rear brake light switch which i replaced. We bled the system and all the brakes worked great.Reset the ABS computer to attempt to shut off the warning lights. Started the bike and took it for a test ride with no problems other than the Abs light starteed blinking again. I parked the bike and left it over night the next day whent to take it for a ride I turn the key and everything is dead except the clock. Here is what I checked
1. Battery at 13 volts but drops drastically if ignition switch is turned on
2. checked ignition switch with ohmeter seems to work properly
3. checked all fuses
4.checked ground connections
5. checked relays and unplugged ABS system no change
Any body have any ideas
Thanks,
Jim

Brand-new batteries fail sometimes - not too often, I agree - but I agree with Paul that you should assess its condition before you go further. If the battery is bad and you think it's good, the rest of your troubleshooting will be for naught. It's a lot easier to make sure now, rather than have to backtrack later.

The symptoms you describe are those shown by a voltage drop from a battery that is not fully charged. That might be because a) the battery is good, but is not fully charged, or b) the battery is defective and incapable of holding a charge. To determine which is the case, disconnect the battery from the rest of the bike's electrical system, either by removing it or just disconnecting one or both of the battery cables. Then charge the battery fully.

The first test assesses what happens to the battery voltage when it addresses a load. Connect a headlight bulb across the fully-charged battery terminals. If after charging, the battery cannot light the bulb or the battery voltage drops significantly when the bulb is connected, the battery is defective because it won't take a charge; the battery should be replaced. If, on the other hand, the bulb lights brightly and the voltage doesn't drop or only drops a little (no more than half a volt) while the bulb is connected, then the battery has taken a charge.

The second test addresses whether the battery can hold a charge. Charge the battery, let the battery sit overnight, and then test it again. If it's significantly less strong the next day, then the battery is again defective because it is incapable of holding a charge. If it passes both tests, then the battery is indeed OK and the electrical system's problem is elsewhere.

With a known good battery (not just an "I believe it's OK because it's new" one), reinstall the battery in the bike and measure the current draw with everything turned off. Only the clock should be drawing current then, and it should draw a very small amount - I'd guess <10 ma. A higher draw tells you that there is a current leak somewhere in the bike's electrical system - worn or crushed insulation on a power-carrying wire within the main wiring harness near the steering head and under a too-tight zip tie is common in K-bikes.

Where are you testing the battery voltage? Right on the two battery terminals? Or on the battery cables? Or some other location?

If on the terminals, the battery is probably at fault. Not properly charged or more likely bad. I've seen several bad "new" batteries. One guy bought a new battery from the bike store and it had less than a half cup of acid in the entire battery.